Data warehousing theory and modelling techniques Building Dimensional Models

1. Matrix Method for getting started Build the Matrix Use the four-step method 1.2

2. Managing the dimensional Modelling Project. 2.1 Data Warehouse Bus Architecture Matrix Fact Table Diagram Fact Table Detail Dimension Table Detail Steps for the Modelling Team Identifying the sources using a Data Modelling Tool 2.7 Summary SummarySummary

Build the Matrix 1.1 n Table Rows : Data Marts Table Rows Table Rows n Table Columns : Dimensions Table Columns Table Columns ExampleExample Data Warehouse Bus Architecture Matrix Example

1.1 Build the Matrix List the Data Marts (rows) n Example: data marts for a telephone co. –customer billing statements –scheduled service and installation orders –trouble reports –marketing promotions –call detail for a billing perspective –customer inventory –labor and payroll –...

1.1 Build the Matrix List the Dimensions (columns) n Example: Dimensions for the telephone co. in data mart: Customer billing statement –Time (date of billing) –Customer –Service –Rate category –Local service provider –...

Data Warehouse Bus Architecture Matrix

Use the four-step Method to design Each Fact Table 1.2 n Step 1. Choose the Data Mart n Step 2. Declare the Grain n Step 3. Choose the Dimensions n Step 4. Choose the Facts Example: Telephone co. Example: Telephone co.Example:

Four-steps e.g.Telephone co. n 1. Data Mart: Customer billing n 2. Grain: the individual line item on each monthly customer bill n 3. Dimensions: Time, Customer, Service, Promotion n 4. Facts: Line item amount, Line item quantity

Fact Table Diagram 2.2 n The fact table Diagram: –Names the fact table –Clearly states its grain –Shows dimensions to which it is connected –Shows all the other dimensions without connections n Example : fact table diagram for the telephone billing line item Example n Example : Supporting information Example : Example :

The telephone billing Fact Table Diagram

Dimension information Table n Supporting information for the Fact Table Diagram includes the Name and Description of each dimension

Fact Table Detail 2.3 n Complete list of all the facts available through the fact table n List includes: –actual facts in the physical table –derived facts presented through views –facts calculated from first two groups n Example: Customer billing Line item fact table detail for the telephone co Example:

Customer billing Line item Fact table detail

Dimension Table Detail 2.4 n Shows attributes in a single dimension n Shows explicit grain of the dimension n Shows the approximate cardinality of each dimension attribute n Shows hierarchies and relationships between the attributes n Example: Time dimension Table detail Example: n Example: Dimension attribute detail descriptions Example:

Time Dimension Table detail diagram

Dimension attribute detail descriptions n Documentation: Full descriptive information to support the diagram –Attribute Name, description, cardinality –Slowly Changing Policy, Sample Values n Example: Time Dimension attribute detail descriptions Example: n Example: Many-to-many relationships and slowly changing dimension attributes Example: n Example: Correlated attributes Example:

Time Dimension attribute detail descriptions

Many-to-many relationships and slowly changing dimension attributes

Correlated attributes

Steps for the Dimensional Modelling Team 2.5 n Create the Initial draft: data marts, dimensions, data matrix and diagrams n Track Base Facts n Track derived Facts (Example) Example n Present initial design to rest of IS team n Select some key users to work on project n Present to Business users

Derived Fact worksheet

Identifying the Sources for Each Fact Table and Dimension Table 2.6 n Source. Name of the source system. n Business owner. Name of the primary contact within the business who is responsible for this data. n IS owner. Name of the person who is responsible. n Platform. Operating environment where system runs. n Location. The actual location of the system. The city and the specific machine where this system runs. n Description. A brief description of what system does n Example: Data Source Definitions Example: n Example: Mapping data from source to Target Example:

Data Source definitions

Mapping data from source to Target Source-to-target data map: n Foundation for the development of the data staging process n To document specifically where the data can be located n Example: Sample Source-to-target data map Example:

Sample Source-to-target data map (1/2)

Sample Source-to-target data map (2/2)  Table name. The name of the logical table in the data warehouse.  Column name. The name of the logical column in the warehouse.  Data type. The data type of the logical column (char, number, date).  Length. The length of the field of the logical column.  Target column description. A description of the logical column.  Source system. The name of the source system where data feeds the target logical column.  Source table/file. The name of the specific table or file where data feeds the target logical column.  Source column/field. The name of the specific column or field where data feeds the target logical column.  Data transform. Notes about any transformations that are required to translate the source information into the format required by the target column.

Using a Data Modelling Tool 2.7 n Used to develop the physical data model n Preferably one that stores your model’s structure in a relational database

Summary (1/2) n Process used to apply dimensional modelling techniques n Bus Architecture Matrix to lay out the data marts and dimensions n Four-step method to design a single data mart n Diagramming techniques n Data sourcing and mapping

Summary (2/2) n In this section we focused on the DATA n Next: different path of lifecycle Technical architecture

Supporting Templates collected on CD-Rom n Template 7.1 Data Mart Matrix n Template 7.2 Dimensional Model Document n Template 7.3 Derived Fact Worksheet n Template 7.4 Logical table design n Template 7.5 Data Source Definition Document n Template 7.6 Source to Target Data Map